β-(1→4)乙酐-D-木聚糖甙酯的合成反应动力学与分子模拟

Synthesis kinetics and molecular simulation of 1,4-beta-D-xylan acetate

根据蔗渣木聚糖β-（1→4）-D-木聚糖与乙酐的酯化反应机理,研究了对甲苯磺酸（PTSA）催化β-（1→4）乙酐-D-木聚糖甙酯的合成反应动力学与分子模拟.讨论了反应温度、催化剂用量及乙酸与乙酐配比等因素对反应过程的影响.研究结果表明,反应温度升高,反应速度显著加快;催化剂用量加大,反应速率常数逐步提高;而乙酸与乙酐配比的改变对反应速率常数的影响不明显.通过积分反应速率方程,对该反应的实验数据进行动力学计算,得到对甲苯磺酸催化β-（1→4）乙酐-D-木聚糖甙酯合成的反应级数为二级,反应表观活化能E_a=33.11 kJ/mol.采用分子动力学模拟方法进行模拟计算,获得了β-（1→4）乙酐-D-木聚糖甙酯的无定形结构与自由体积模型,为β-（1→4）乙酐-D-木聚糖甙酯的抗HIV活性研究奠定了微观结构基础.

According to the esterification mechanism of 1,4-beta-D-xylan and acetic anhydride, the reaction kinetics and molecular simulation have been studied with p-toluene sulfonic acid as catalyst. The effects of reaction temperature, content of catalyst and the mass ratio of acetic acid to acetic anhydride on apparent reaction rate constants were also investigated. The results showed that the rate of reaction is obviously accelerated with the increasing of temperature, the reaction rate constant gradually increased with the increasing of catalyst dosage, while the mass ratio of acetic acid to acetic anhydride has no effect on the reaction rate constant. The reaction between 1,4-beta-D-xylan and acetic anhydride was a second-order reaction with p-toluene sulfonic acid as catalyst, and the activation engery（E_a） of the reaction was 33.11 kJ/mol by the kinetic calculation of the experimental data according to the integrated reaction rate equation. The 1,4-beta-D-xylan ester derivatives were simulated and its transition states were searched by the method of molecular dynamics simulation, and the amorphous structure and the free volume model of the xylan acetate derivatives were obtained. These provide a microstructure foundation for the anti-HIV activity of the 1,4-beta-D-xylan acetate.